Antineoplastic agents, used for treatment of solid cancers such as lung cancer or digestive organ carcinomas and blood cancers such as leukemia, are systemically administered through routes of administration such as intravenous or oral administration, and then, are distributed to certain tumorous sites and inhibit or suppress the proliferation of cancer cells to exhibit their therapeutic efficacy. However, the systemically-administered antineoplastic agents are rapidly taken into livers and reticuloendothelial organs from blood, or rapidly excreted into urine, and accordingly, their blood concentrations may be sometimes too low to distribute to tumorous sites sufficiently. In addition, common antineoplastic agents themselves do not distribute tumorous sites selectively (tumor selectivity), and therefore, the antineoplastic agents are uniformly distributed over various tissues and cells of the whole body and act as cytotoxins also against normal cells and tissues, which results in problems of the appearance of adverse effects, e.g., emesis, pyrexia, or alopecia at an extremely high rate. Therefore, it has been desired to develop a means of efficiently and selectively distributing antineoplastic agents to tumorous sites.
As one of such means, a process was proposed in which a polysaccharide derivative having carboxyl groups is used as a polymer carrier, and an antineoplastic agent is bound to the polymer carrier to delay the disappearance of the antineoplastic agent from blood and to enhance selectivity to tumor tissues. For example, International Publication WO94/19376 discloses a DDS compound in which a peptide chain (the number of amino acid residues: 1 to 8) is bound to a carboxyl group of a polysaccharide having carboxyl groups, and doxorubicin, daunorubicin, mitomycin C, bleomycin or the like is further bound by means of the peptide chain. In addition, Japanese Patent Publication (KOKOKU) No. (Hei) 7-84481/1995 discloses a DDS compound in which the aforementioned antineoplastic agent is introduced into a carboxymethylated mannoglucan derivative by means of a Schiff base or an acid amide bond.
These DDS compounds (also referred to as “drug complexes”) are characterized in that they have more excellent antineoplastic activity, reduced toxicity and adverse effects compared to antineoplastic agents, per se, that are bound to polymer carriers. The inventors of the present invention have provided a DDS compound which is formed by binding a polymer carrier such as polysaccharide compounds to a drug compound such as antineoplastic agents by means of a spacer consisting of one to eight amino acids, and which can site-selectively distribute the drug compound such as antineoplastic agents to target tissues (International Publication WO97/46260). They have also found that a carboxy(C1-4)alkyldextran polyalcohol has highly desirable characteristics as a polymer carrier, and provided a DDS compound containing a carboxy(C1-4)alkyldextran polyalcohol as a polymer carrier (the above mentioned International Publication).
As for technologies relating to DDS compounds utilizing polyalcoholized polysaccharide derivatives as polymer carriers, some reports are available, for example, “Researches on polysaccharide-peptide-doxorubicin complexes—Correlations between stabilities of polysaccharide carriers in blood and their anti-neoplastic activities” (Abstracts of 10th Meeting of the Japan Society of Drug Delivery System, 279, 1994); “Researches on polysaccharide-peptide-doxorubicin complexes—Pharmacokinetics and anti-neoplastic activity” (Abstracts of 9th Annual Meeting of Japanese Society for the study of xenobiotics, 292, 1994); Abstracts of 19th Seminar of Trends in Research and Development (held by The Organization for Pharmaceutical Safety and Research), D-9, 1995; and “Researches on drug delivery to a tumor tissue by polysaccharide carriers” (Abstracts of 12th Colloid and Interface Technology Symposium, The Chemical Society of Japan, 51, 1995).
As means for enhancing organ selectivity of polysaccharide compounds and the like, for example, saccharide-modified polyglutamic acid derivatives (Japanese Patent Unexamined Publication (KOKAI) (Hei) No. 5-178986/1993), saccharide-modified polylysine derivatives (Japanese Patent Un-examined Publication (KOKAI) (Hei) No. 5-222187/1993), D-galactopyranosylgluconic acid derivatives of a poly-ε-substituted-L-lysine (Japanese Patent Unexamined Publication (KOKAI) (Hei) No. 7-70311/1995), saccharide-modified poly-ω-substituted-L-glutamic acid derivatives (Japanese Patent Unexamined Publication (KOKAI) (Hei) No. 7-228688/1995), polysaccharide compounds bound to a saccharide compound by means of a linker (Japanese Patent Unexamined Publication (KOKAI) (Hei) No. 8-85703/1996), glucosyl-protein derivatives (Japanese Patent Un-examined Publication (KOKAI) (Hei) No. 9-118699/1997) and the like have been known. However, any techniques for enhancing organ selectivity of DDS compounds have not polymer carrier.
When a DDS compound is clinically used in which a polymer carrier and a residue of a drug compound are linked to each other by means of a spacer containing an oligopeptide, it is necessary to accurately measure a blood concentration of the DDS compound, per se, and also to accurately measure a content of the residue of the drug compound, such as antineoplastic agents introduced to the DDS compound, to determine an appropriate dosage or to test lot differences of products. The measurements of a blood concentration of a DDS compound and a content of residue of a drug compound in the DDS compound have conventionally been performed by measuring the DDS compound directly, per se, based on fluorescence of the drug compound or its UV absorption without cleaving the drug compound or the drug compound bound with a part of the spacer from the DDS compound. Furthermore, a method based on NMR analysis of a DDS compound, per se, and a method of measuring a decomposed product obtained by an acid treatment of a DDS compound have also been proposed.
However, those methods have problems in that a quantitative measurement of a decomposed product by an acid treatment cannot be performed when the drug compound is susceptible to an acid, and accuracy of the NMR analysis is insufficient. Moreover, UV absorption of a residue of a drug compound present in a DDS compound may cause a shift of maximum absorption wavelength or a change in molar extinction coefficient relative to the drug compound itself because of effects of a polymer carrier or a peptide spacer, and therefore, it is generally difficult to accurately measure a content of a residue of a drug compound introduced into a DDS compound. It is extremely difficult to quantitatively measure a DDS compound in tissues after administration to living bodies by the methods based on NMR analysis or UV absorption.